They are fitted, yes. Both the body and arms are narrow.
We will have some photos of them being worn by the weekend.
In the meantime, the mannequin (with a 38" chest) is wearing a size small. There is a shirt worn underneath, and it is a comfortable fit with plenty room to move and breath (were the mannequin able). With a thick jumper underneath, the small would not suffice — it'd have to be a medium.
The measurements of the garments on our site are all done by hand, and are precise, so if in doubt, you should fine them a reliable guide.